Rotary electric machine with air gaps configured to cancel torque pulsations

ABSTRACT

A rotary electric machine includes a stator having stator windings; and a rotor rotatably disposed in the stator, said rotor having a rotor core provided with a plurality of magnets and a plurality of magnetic auxiliary salient poles formed between poles of the magnets. In this rotary electric machine: a magnetic air gap is provided in an axial direction of the rotor in a position shifted in a circumferential direction from a q axis passing through a center of the magnetic auxiliary salient pole within the magnetic auxiliary salient pole; and an amount of shifting the magnetic air gap from the q axis in the circumferential direction differs according to a position of the magnetic air gap in the axial direction so as to cancel torque pulsation in energization caused due to the magnetic air gap.

This application is a continuation of U.S. patent application Ser. No.12/389,233, filed Feb. 19, 2009, which in turn claims the priority ofJapanese application JP 2008-053572 filed on Mar. 4, 2008. The entiredisclosure of each of the above-identified applications is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary electric machine, and anelectric vehicle including the same.

2. Description of the Related Art

Drive motors used for electric vehicles or hybrid vehicles are requiredto output large power. Thus, permanent magnet type motors using asintered magnet made of rare earth material for holding large energy isgenerally used. An embedded magnet type motor among the permanent magnettype motors is used as the drive motor which can satisfy requirements,including low-speed and large-torque output, and a wide range ofrotation speeds.

Torque pulsation of the motor causes noise or vibration. In particular,the torque pulsation on the low-speed side of the electric vehicledisadvantageously deteriorates ride quality. In a conventional motor, apermanent magnet is generally skewed so as to reduce cogging torque.Instead of skewing the permanent magnet, JP-A-2005-176424 has proposedthat a rotary electric machine is provided with slots on the outerperipheral side of the embedded magnet or the outer peripheral surfaceof a pole piece so as to reduce the cogging torque such that the slot isformed to be shifted in the direction of rotation as viewed from thedirection of a rotation axis.

The occurrence of torque pulsation in a rotary electric machine iscaused by the cogging torque due to a magnetic circuit for allowing amagnetic flux generated from a permanent magnet provided in a rotor topass through a stator and then to return to the rotor again, and by arotating magnetic flux generated by a current of the stator. Theabove-mentioned JP-A-176424/2005 relates to a technique for reducing thecogging torque as mentioned above.

The invention is directed to reduction of the pulsation due to therotating magnetic flux generated by the stator current as mentionedabove.

When the method disclosed in the above-mentioned JP-A-176424/2005 isintended to be used for reducing torque pulsation due to the statorcurrent, which is to be solved by the invention, the appropriatereduction of the cogging torque becomes very difficult. That is, themethod disclosed in JP-A-176424/2005 is designed to reduce the coggingtorque. When the concept of this method is intended to be furtherapplied so as to reduce the torque pulsation due to the stator current,the inherent cogging torque cannot be appropriately reduced.

General techniques proposed for reducing torque pulsation have the sameinfluence on both of the cogging torque and the torque pulsation due tothe stator current. As a result, in order to reduce both torquepulsations, it is necessary to handle the rotary electric machine takinginto consideration the influence on both. This makes it difficult toeasily solve both pulsations.

The inventors have thought that the entire torque pulsation can be moreeasily reduced and adjusted if the torque pulsation due to the statorcurrent can be reduced by a structure or way which has little influenceon the cogging torque. For example, when the cogging torque can bereduced and additionally the torque pulsation due to the stator currentcan also be reduced, the entire torque pulsation can be easily reduced.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a techniquewhich can reduce the torque pulsation due to the stator current by a wayor structure which has little influence on the cogging toque.

In order to achieve the object described above, according to a firstaspect of the present invention, there is provided a rotary electricmachine including: a stator having stator windings; and a rotorrotatably disposed in the stator, said rotor having a rotor coreprovided with a plurality of magnets and a plurality of magneticauxiliary salient poles formed between poles of the magnets, wherein amagnetic air gap is provided in an axial direction of the rotor in aposition shifted in a circumferential direction from a q axis passingthrough a center of the magnetic auxiliary salient pole within themagnetic auxiliary salient pole, and wherein an amount of shifting themagnetic air gap from the q axis in the circumferential directiondiffers according to a position of the magnetic air gap in the axialdirection so as to cancel torque pulsation in energization caused due tothe magnetic air gap.

It is preferable that circumferential positions of the magnets in therotor core are constant regardless of the axial positions of themagnets.

Further, it is preferable that the rotor core is divided into aplurality of division cores provided in the axial direction, each ofsaid division cores having the magnet, the magnet auxiliary salientpole, and the magnetic air gap, and that the circumferential positionsof the magnets in the division cores are constant regardless of theaxial positions of the magnets.

Further, it is preferable that the rotary electric machine furtherincludes a plurality of core groups, said core group including divisioncores having the magnetic air gaps located substantially in the samerespective circumferential positions, and that the total thicknesses inthe axial direction of the respective core groups are substantially thesame.

Further, it is preferable that the rotary electric machine furtherincludes two core groups with the magnetic air gaps located in differentrespective circumferential positions, and that phases of torquepulsations generated by the respective two core groups are shifted by 15degrees or 30 degrees in terms of electrical angle.

Further, it is preferable that the rotary electric machine furtherincludes first, second, and third core groups with the magnetic air gapslocated in different respective circumferential positions, and thatphases of torque pulsations respectively generated by the first, second,and third core groups are shifted by 10 degrees or 20 degrees in termsof electrical angle between the first core group and the second coregroup, and between the second core group and the third core group,respectively.

Further, it is preferable that the magnetic air gap is a concave portionformed at the surface of the rotor core, or a hole formed in the rotarycore.

Further, it is preferable that a circumferential angle of the concaveportion is set equal to or less than one half a peripheral length of anauxiliary salient pole.

Further, it is preferable that the hole serving as the magnetic air gapis integrally formed with a hole having the magnet provided therein.

Further, it is preferable that the plurality of magnets each of whosemagnetization directions is a radial direction of the rotor core arearranged in the circumferential direction such that the magnetizationdirections are alternately reversed.

Further, it is preferable that the respective magnets constitute amagnet group including a plurality of magnets whose magnetizationdirections are substantially equal.

Further, it is preferable that the magnetic auxiliary salient poles areprovided with a plurality of the magnet air gaps.

Further, it is preferable that the rotor core is formed by laminatingelectromagnetic steel plates, each plate having a hole or a cutoutformed therein for forming the magnetic air gap.

Further, it is preferable that the two types of magnetic air gapslocated in different circumferential positions are formed in the rotorcore by laminating one steel plate on another steel plate turned upsidedown.

According to a second aspect of the present invention, there is providedan electric vehicle including: the rotary electric machine according tothe first aspect; a battery for supplying a direct-current power; and aconverter for converting the direct-current power of the battery into analternating-current power, and supplying the alternating-current powerto the rotary electric machine, wherein the electric vehicle is traveledby a drive force of the rotary electric machine.

According to the configuration of the present invention, the torquepulsation caused in relation to the stator current supplied to a statorwinding can be reduced by the way or structure which has littleinfluence on the cogging torque.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described with reference to the accompanyingdrawings in which:

FIG. 1 is a diagram showing a schematic construction of a hybridelectric vehicle equipped with a rotary electric machine according toone embodiment of the invention;

FIG. 2 is a circuit diagram of a power converter 600;

FIG. 3 is a sectional view of the rotary electric machine according tothe embodiment;

FIG. 4 is a perspective view showing an external appearance of a stator230;

FIG. 5A is a perspective view of a rotor core 252;

FIG. 5B is an exploded perspective view of the rotor core 252;

FIG. 6A is a sectional view of the stator 230 and a rotor 250 takenalong the line A-A passing through a core 301;

FIG. 6B is a sectional view of the stator 230 and a rotor 250 takenalong the line B-B passing through a core 302;

FIG. 7A is an enlarged sectional view of the vicinity of a permanentmagnet 254 b taken along the line A-A;

FIG. 7B is an enlarged sectional view of the vicinity of the permanentmagnet 254 b taken along the line B-B;

FIG. 8 is a diagram explaining a reluctance torque;

FIG. 9 is a diagram showing the distribution of magnetic flux innon-energization;

FIG. 10A is a property diagram of a waveform of a cogging torque innon-energization;

FIG. 10B is a property diagram of a waveform of an induced voltage innon-energization;

FIG. 11 is a diagram showing the distribution of magnetic flux takenalong the line A-A in energization;

FIG. 12 is a diagram showing the distribution of magnetic flux takenalong the line B-B in energization;

FIG. 13 is a diagram showing a waveform of the torque pulsation inenergization;

FIG. 14 is a sectional view showing parts of the stator 232 and therotor 250 for explaining the reduction of cogging torque;

FIG. 15 is a diagram showing a relationship between a cogging torque anda rate of a magnetic pole arc degree τg/τp;

FIG. 16 shows a maximum torque when the magnet pole arc degree τm/τp anda magnet hole pole arc degree τg/τp are changed;

FIG. 17A is a perspective view of the skewed rotor 250, which is dividedinto two parts in the axial direction;

FIG. 17B is a perspective view of the skewed rotor 250, which is dividedinto three parts in the axial direction;

FIG. 18A shows one of four kinds of methods for laminating and skewingdivided cores of the rotor;

FIG. 18B shows one of four kinds of methods for laminating and skewingdivided cores of the rotor;

FIG. 18C shows one of four kinds of methods for laminating and skewingdivided cores of the rotor;

FIG. 18D shows one of four kinds of methods for laminating and skewingdivided cores of the rotor;

FIG. 19A shows a continuous skew when a skew direction is reversed inmidstream;

FIG. 19B shows a continuous skew when the skew direction is fixed to onedirection;

FIG. 20 is a sectional view of the rotor 250 of a surface magnet type;

FIG. 21 is a sectional view showing the stator 232 and the rotor 250 inthe case of concentrated winding;

FIG. 22A is a sectional view of the rotor 250 according to a secondembodiment, taken along the line A-A;

FIG. 22B is a sectional view of the rotor 250 according to the secondembodiment, taken along the line B-B;

FIG. 23A is a sectional view showing another example of the rotor 250according to the second embodiment, taken along the line A-A;

FIG. 23B is a sectional view showing another example of the rotor 250according to the second embodiment, taken along the line B-B;

FIG. 24 is a sectional view of the rotor 250 including a pair ofpermanent magnets 254 arranged in a V-like shape;

FIG. 25A is a sectional view of the rotor 250 according to a thirdembodiment, taken along the line A-A;

FIG. 25B is a sectional view of the rotor 250 according to the thirdembodiment, taken along the line B-B;

FIG. 26 is a sectional view of a rotary electric machine having oil 403for cooling in a housing 234;

FIG. 27 is a diagram showing an external appearance of a rotor core 252according to a fourth embodiment;

FIG. 28 is a partial sectional view of a core 301 according to thefourth embodiment;

FIG. 29 is a partial sectional view of a core 302 according to thefourth embodiment;

FIG. 30 is a partial sectional view of another partially different core301 according to the fourth embodiment;

FIG. 31 is a partial sectional view of a further partially differentcore 302 according to the fourth embodiment; and

FIG. 32 is a partially explanatory diagram of the core 301 shown in FIG.31.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following embodiments can solve not only the problems associatedwith the above-mentioned object of the invention, but also otherproblems. Now, the representative problems to be solved by theembodiments, some of which are the same as those associated with theobject of the invention, and a basic structure in relation to thesolving of the problems will be described below.

(Good Torque Properties as Drive Rotary Electric Machine for Vehicle)

A rotary electric machine for driving a vehicle is required to outputhigh torque in a start state of rotation or in a low-speed rotationregion. Further, the torque output is also required even in a high-speedrotation region of the rotary electric machine. For example, the torqueoutput is apparently necessary at 6000 rpm or more. The torque output isrequired at 10000 rpm or more. The electric motor which can be used at12000 rpm makes the driving of the vehicle more preferable.

When the torque output in the low speed rotation region including therotation start state is intended to be generated by magnet torque of apermanent magnet, the amount of use of the magnet becomes large.Further, an induced voltage induced based on the magnetic flux generatedby the permanent magnet in the high-speed rotation region becomes high,which makes it difficult to supply the power to the rotary electricmachine and thus needs a very high power supply voltage. That is, it isdifficult to greatly increase the power supply voltage. This makes itdifficult to obtain the torque output in a relatively high-speedrotation region, for example, at 6000 rpm or more.

In the embodiment to be described later, when the axis of the permanentmagnet is set as the d axis, a magnetic resistance in the q-axisdirection is made small, which generates large reluctance torque. Therequired torque consists of both magnet torque and reluctance torque, sothat the ratio of the magnet torque to the required torque can be small.For example, when about 30 to 50% or more, or about 55% of the requiredtorque can be the reluctance torque, the magnet torque can be reduced bya degree corresponding to the ratio, which can decrease the amount ofpermanent magnet material. Thus, the induced voltage by the permanentmagnet in the high speed rotation can be decreased, which facilitatessupply of the power from an inverter even in the high speed rotation,and can generate rotary torque even in the high speed rotation. Therotary electric machines of the following embodiments have a structurewhich can effectively generate the reluctance torque, and thus canoutput the rotary torque even in the above high-speed rotation region aswell as the large rotary torque in the low-speed rotation region.

The rotation region capable of driving a vehicle is widened, whereby,for example, a hybrid vehicle having a narrow rotation region owned byan engine can be driven well, which leads to improvement of the fuelefficiency of the vehicle. Further, the decrease in amount of permanentmagnet material can reduce no-load loss of the rotary electric machine,leading to improvement of efficiency of traveling of the vehicle.

(Downsizing)

The drive rotary electric machine for a vehicle is desired to have itsvolume downsized in addition to having the above torque properties. Inthis embodiment, the number of magnetic poles of the rotor is equal toor more than eight, which is advantageous in downsizing and high output.Since the number of the magnetic poles of the rotor is equal to or morethan eight, a magnetic circuit generated in the stator tends to beformed near a portion of a stator core near the rotor. Thus, the lengthof the stator core in the radial direction thereof can be reduced. Thisdecreases the length of the stator in the radial direction, that is, thedimension in the radial direction through the center axis of a sectionperpendicular to a rotary shaft.

(Reduction of Pulsation)

The reduction of torque pulsation has been described in theabove-mentioned paragraphs of the effect of the invention and theproblems to be solved by the invention. The reduction of torquepulsation performed by the following embodiments will be describedspecifically below. The embodiments to be described later canrespectively reduce the cogging torque and the torque pulsation due tothe stator current.

(1) Reduction of Cogging Torque

In a structure having a permanent magnet embedded in a rotary core, amagnetic flux density in the direction of rotation of a gap between arotor and a stator tends to drastically change at an end of thepermanent magnet in the rotation direction (which can also be describedas “an end in the circumferential direction”), which may cause coggingtorque. In the following embodiments, a magnetic air gap 257 is providedat an end of the permanent magnet corresponding to an end of a rotormagnetic pole (field pole) formed by the permanent magnet. The magneticair gap 257 can reduce a drastic change in magnetic flux density of agap between the above rotor and stator in the rotation direction. Themagnetic air gap 257 can have an effect of decreasing the coggingtorque.

(2) Reduction of Pulsation Due to Stator Current

In the following embodiments, a magnetic air gap 258 is formed in anauxiliary magnetic pole (auxiliary salient pole 259) for forming amagnetic circuit on the q axis. The positions of the magnetic air gaps258 are changed in the rotation direction as viewed along the directionof a rotary shaft. Such an arrangement can reduce the pulsation due tothe stator current.

(3) Reduction of Pulsation Due to Stator Current by Structure HavingLittle Influence on Cogging Torque

The conventional technique of reducing the torque pulsation hasinfluences on both the cogging torque and the pulsation due to thestator current. When the cogging torque is intended to be reduced, theeffect of reducing the pulsation due to the stator current becomesinsufficient, or too sufficient. Thus, it is necessary to find out suchconditions that can reduce both torque pulsations by repeatingexperiments. That is, even when an optimal condition for reducing thepulsation due to the stator current is found out, the condition is notalways preferable for reduction of the cogging torque, and may beundesired one in many cases. Thus, it is very difficult to find acondition that can reduce both torque pulsations. Even if the preferablecondition is found out, the condition tends to change depending onvarious factors. Every time a new rotary electric machine is designed,the experiment needs to be repeated. The solving means described in theabove paragraph (2) has very little influence on the cogging torque.When a condition for reduction of the pulsation due to the statorcurrent is adjusted, the adjustment cannot deteriorate the state of thecogging torque. This reduces the torque pulsation very easily.

(Improvement of Efficiency of Rotary Electric Machine)

In the embodiment to be described below, the length of a magnetic bridgecan be increased, which can reduce a leakage magnetic flux of thepermanent magnet, leading to improvement of the efficiency of the rotaryelectric motor. The magnetic bridges can be formed along the magneticair gaps 257 or slots 282 provided on both ends of the field pole,thereby preventing the concentration of stress, resulting in a decreasedsectional area of the magnetic flux, which leads to improvement of theefficiency.

(Improvement of Productivity)

The external appearance of the rotary electric machine in an embodimentto be described later can be produced by punching using a silicon steelplate. Thus, the embodiment has excellent productivity. A core 301 hasthe shape symmetric with respect to that of the core 302 as will bedescribed later. One silicon steel plate subjected to punching can beturned upside down to be used as the other core. As a result, the numberof types of cores to be produced can be decreased to improve theproductivity.

In the embodiments to be described, magnets introduced into the rotaryelectric machine along the axial direction of the rotor are disposedwithout being shifted in the circumferential direction, or are hardlydisplaced in the circumferential direction, which facilitates amagnetization work, thereby improving productivity. As will be describedlater, the permanent magnet may be magnetized, and then embedded in therotor core. Alternatively, the permanent magnet may be inserted into therotary core before being magnetized, and then magnetized by applying astrong magnetic field to the magnet. The latter does not interrupt aninsertion work of the magnets because of an attraction force of themagnets in insertion of the magnets, and can suppress adhesion ofcontaminant or the like, thereby further improving the productivity. Inemploying such a magnetization method, when the magnet is axiallydivided into parts shifted from each other in the circumferentialdirection, each magnet part divided may be separately magnetized so asto improve magnetization properties. In the embodiment described later,the magnet is not divided in the axial direction, or the number ofdivision of the magnet is small, which can reduce the number ofrepeating of the magnetization work, thereby improving the productivity.In the case of magnetizing a magnet extending in the axial direction atone time, nonuniform magnetization hardly occurs due to an influence,such as a difference in distance up to a magnetization device, and canimprove the magnet properties and productivity as compared to the casein which the magnet is axially divided to be shifted from each other inthe circumferential direction.

Now, preferred embodiments for implementing the invention will bedescribed below with reference to the accompanying drawings. The rotaryelectric machine of the invention can respectively reduce the coggingtorque in non-energization and the torque pulsation in energization,thereby achieving reduction in size, cost, and torque pulsation as willbe described later. Thus, for example, the rotary electric machine issuitable for use as a motor for traveling an electric vehicle. Therotary electric machine of the invention can provide an electric vehiclehaving low vibration, low noise, and good ride quality. The rotaryelectric machine of the invention can be applied to a pure electricvehicle which is run only by the rotary electric machine, and a hybridelectric vehicle driven by both the engine and the rotary electricmachine. Now, the hybrid electric vehicle will be described as oneexample.

First Embodiment

FIG. 1 is a diagram showing a schematic construction of a hybridelectric vehicle equipped with the rotary electric machine according toone embodiment of the invention. A vehicle 100 is equipped with anengine 120, a first rotary electric machine 200, a second rotaryelectric machine 202, and a battery 180. The battery 180 suppliesdirect-current power to a power converter (inverter) 600 for driving therotary electric machines 200 and 202 when driving forces for themachines 200 and 202 are necessary. The power converter 600 converts thedirect-current power into alternating-current power, and respectivelysupplies the converted alternating-current power to the rotary electricmachines 200 and 202. In regeneration traveling, the rotary electricmachines 200 and 202 generate alternating-current power based on kineticenergy of the vehicle to supply the power to the power converter 600.The power converter 600 converts the alternating-current power intodirect-current power to supply the direct-current power to the battery810. A battery (not shown) for supplying low-voltage power (for example,14 volt power) is mounted on the vehicle, and thus the direct-currentpower of a constant voltage is supplied to a control circuit to bedescribed later.

The rotary torques of the engine 120 and the rotary electric machines200 and 202 are transferred to front wheels 110 via a transmission 130,and a differential gear 132. The transmission 130 is controlled by atransmission controller 134, and the engine 120 is controlled by anengine controller 124. The battery 180 is controlled by a batterycontroller 184. The transmission controller 134, the engine controller124, the battery controller 184, the power converter 600, and anintegrated controller 170 are connected to one another via acommunication line 174.

The integrated controller 170 receives information about states ofrespective low-level controllers with respect to the integratedcontroller 170, that is, the transmission controller 134, the enginecontroller 124, the power converter 600, and the battery controller 184,from these controllers via the communication line 174. The integratedcontroller 170 computes a control command of each controller based onsuch information. The control command computed is transmitted to thecorresponding controller via the communication line 174.

The battery 180 having a high voltage is constructed of a secondarybattery, such as a lithium ion battery or a nickel hydride battery, andoutputs a direct-current power of high voltage of 250 to 600 volts ormore. The battery controller 184 outputs information about a dischargestate of the battery 118 and a state of each unit cell constituting thebattery 18 to the integrated controller 170 via the communication line174.

The integrated controller 170 gives an instruction of a power generatingoperation to the power converter 600 when the charging of the battery180 is determined to be necessary based on the information from thebattery controller 184. The integrated controller 170 mainly managesoutput torques of the engine 120 and the rotary electric machines 200and 202, computes a total torque of the output torque of the engine 120and the output torques of the rotary electric machines 200 and 202, or atorque distribution ratio between these torques, and transmits controlcommands to the transmission controller 134, the engine controller 124,and the power converter 600 based on the result of the computation. Thepower converter 600 controls the rotary electric machines 200 and 202 soas to provide the torque output or generated power based on a torquecommand from the integrated controller 170 according to the command.

The power converter 600 is provided with a power semiconductorconstituting an inverter so as to drive the rotary electric machines 200and 202. The power converter 600 controls a switching operation of thepower semiconductor based on the command from the integrated controller170. Such a switching operation of the power semiconductor causes therotary electric machines 200 and 202 to be driven as an electric motoror a generator.

When the rotary electric machines 200 and 202 are operated as anelectric motor, the direct-current power from the high-voltage battery180 is supplied to a direct-current terminal of the inverter of thepower converter 600. The power converter 600 controls the switchingoperation of the power semiconductor to convert the supplieddirect-current power into a three-phase alternating-current power, andthen to supply the alternating-current power to the rotary electricmachines 200 and 202. On the other hand, when the rotary electricmachines 200 and 202 are operated as the generator, the rotors of therotary electric machines 200 and 202 are rotatably driven by rotarytorque added from the outside, whereby the three-phasealternating-current power is generated in stator windings of the rotaryelectric machines 200 and 202. The generated three-phasealternating-current power is converted into direct-current power by thepower converter 600, and the direct-current power is supplied to thehigh-voltage battery 180, so that the battery is charged.

The rotary electric machine 200 and the rotary electric machine 202 areindependently controlled. For example, when the rotary electric machine200 is operated as the electric motor, the rotary electric machine 202can be operated as the electric motor, and also as the generator, andfurther can be stopped. It is apparent that the opposite is also true.The integrated controller 170 determines in which mode each of therotary electric machines 200 and 202 is operated, and gives a command tothe power converter 600. Based on the command, the power converter 600is in an operating mode of the electric motor, or in an operating modeof the generator, or in a stopped mode of operation.

FIG. 2 schematically shows a circuit diagram of the power converter 600shown in FIG. 1. The power converter 600 is provided with a firstinverter for the rotary electric machine 200 and a second inverter forthe rotary electric machine 202. The first inverter includes a powermodule 610, a first drive circuit 652 for controlling a switchingoperation of each power semiconductor 21 of the power module 610, and acurrent sensor 660 for detecting a current of the rotary electricmachine 200. The drive circuit 652 is provided in a drive circuitsubstrate 650. On the other hand, the second inverter includes a powermodule 620, a second drive circuit 656 for controlling a switchingoperation of each power semiconductor 21 of the power module 620, and acurrent sensor 662 for detecting a current of the rotary electricmachine 202. The drive circuit 656 is provided in a drive circuitsubstrate 654. The control circuit 648 provided in a control circuitsubstrate 646, a condenser module 630, and a transmitting and receivingcircuit 644 mounted on a connector substrate 642 are commonly sharedbetween the first inverter and the second inverter.

The power modules 610 and 620 are operated according to drive signalsoutput from the respective drive circuits 652 and 656. The power modules610 and 620 respectively convert direct-current power supplied from thebattery 180 into three-phase alternating-current power, and supply thepower to the stator windings, which are armature windings of therespective rotary electric machines 200 and 202. The power modules 610and 620 converts alternating-current power induced in the statorwindings of the rotary electric machines 200 and 202 into directcurrent, and supplies the direct current to the high-voltage battery180.

The power modules 610 and 620 include three-phase bridge circuits asshown in FIG. 2, and series circuits corresponding to the three-phasecircuits are electrically connected in parallel between a positiveelectrode and a negative electrode of the battery 180. Each seriescircuit includes a power semiconductor 21 constituting an upper arm anda power semiconductor 21 constituting a lower arm. These powersemiconductors 21 are connected in series to each other. The powermodule 610 and the power module 620 have substantially the same circuitconfiguration as shown in FIG. 2. Here, the power module 610 will bedescribed below as a representative.

In this embodiment, an insulated gate bipolar transistor (IGBT) 21 isused as a power semiconductor element for switching. The IGBT21 includesthree electrodes, namely, a collector electrode, an emitter electrode,and a gate electrode. A diode 38 is electrically connected to betweenthe collector electrode and the emitter electrode of the IGBT 21. Thediode 38 includes two electrodes, namely, a cathode electrode and ananode electrode. The cathode electrode is electrically connected to thecollector electrode of the IGBT 21 and the anode electrode iselectrically connected to the emitter electrode of the IGBT 21 such thata direction from the emitter electrode to the collector electrode of theIGBT 21 is the forward direction.

A metal-oxide semiconductor field-effect transistor (MOSFET) may be usedas a power semiconductor element for switching. The MOSFET has threeelectrodes, namely, a drain electrode, a source electrode, and a gateelectrode. The MOSFET has a parasitic diode between the source electrodeand the drain electrode such that the direction from the drain electrodeto the source electrode is the forward direction, and thus does not needto have the diode 38 shown in FIG. 2.

The arm of each phase is constructed by electrically connecting thesource electrode of the IGBT21 to the drain electrode of the IGBT21 inseries. Although only one IGBT of each of the upper and lower arms ofthe respective phases is shown in this embodiment, a plurality of IGBTsare electrically connected in fact in parallel because a currentcapacity to be controlled is large. For simplification, one powersemiconductor will be described below.

In an example shown in FIG. 2, each of the upper and lower arms of therespective phases is constructed of three IGBTs. The drain electrode ofthe IGBT21 of each upper arm of each phase is electrically connected tothe positive electrode of the battery 180, and the source electrode ofthe IGBT21 of each lower arm of each phase is electrically connected tothe negative electrode of the battery 180. An intermediate point of eacharm of the phase (a connection portion between the source electrode ofthe IGBT on the upper arm side and the drain electrode of the IGBT onthe lower arm side) is electrically connected to an armature winding(stator winding) of the corresponding phase of each of the rotaryelectric machines 200 and 202.

Drive circuits 652 and 656 constitutes drive units for controlling therespective inverters 610 and 620, and generate drive signals for drivingthe IBGTs 21 based on a control signal output from the control circuit648. The drive signals generated by the drive circuits 652 and 656 arerespectively output to the gates of the respective power semiconductorelements of the power modules 610 and 620. Each of the drive circuits652 and 656 is provided with six integrated circuits for generating thedrive signal to be supplied to the gate of each of the upper and lowerarms of each phase. The six integrated circuits are constructed as oneblock.

A control circuit 648 constitutes a controller for each of the inverters610 and 620. The control circuit 648 is constructed of a microcomputerfor computing a control signal (control value) for operating (turning onand off) the power semiconductor elements for switching. The controlcircuit 648 receives inputs of a torque command signal (torque commandvalue) from a high-level controller, sensor outputs from the electriccurrent sensors 660 and 662, and sensor outputs from the rotary sensorsmounted on the rotary electric machines 200 and 202. The control circuit648 computes the control value based on the input signals, and outputscontrol signals for controlling switching timing of the drive circuits652 and 656.

The transmitting and receiving circuit 644 mounted on the connectorsubstrate 642 is to electrically connect the power converter 600 to theexternal controller, and transmits and receives information with anotherdevice via the communication line 174 shown in FIG. 1. The condensermodule 630 constitutes a smoothing circuit for suppressing variations indirect-current voltage generated by the switching operation of the IGBT21. The condenser 630 is electrically connected in parallel to terminalson the direct-current side of the first and second power modules 610 and620.

FIG. 3 is a sectional view of the rotary electric machine 200 or 202shown in FIG. 1. The rotary electric motor 200 has substantially thesame structure as that of the rotary electric motor 202. Now, thestructure of the rotary electric machine 200 will be described below asthe representative. The structure to be described later does not need tobe used in both rotary electric machines 200 and 202, and thus may beused in at least one of them.

A stator 230 is held in the housing 212, and includes a stator core 232and stator windings 238. A rotor 250 is rotatably held via an air gap222 inside the stator core 232. The rotor 250 includes a rotor core 252and a permanent magnet 254. The rotor core 252 is fixed to a shaft 218.The housing 212 has a pair of end brackets 214 with bearings 216provided therein, and the shaft 218 is rotatably held by the bearings216. The stator core 232 is made by laminating a number of magneticsteel plates, for example, silicon steel plates, each having a thicknessof 0.2 to 0.35 millimeters. The lamination of thin steel plates cansuppress the occurrence of eddy current, thus reducing iron loss. Thereduction of iron loss is very important to a rotary electric machineused in the high-speed rotation region, such as that of this embodiment.

FIG. 4 is a diagram showing an external appearance of the stator 230.The stator windings 238 provided in the stator 230 are formed bydistributed winding of coils 233. A magnetic field formed by the statorwindings 238 distributed and wound has the magnetic flux distributionsubstantially in the shape of a sine wave. Thus, the rotary electricmachine employing the distributed winding stator 230 easily obtains thereluctance torque, and is appropriated for obtaining a motor propertyfor an electric vehicle or the like. In this embodiment, the statorincluding the distributed winding type stator windings will be mainlydescribed as an example. Although a concentrated winding type statewinding has a slightly worse electric property, it can be used.

As shown in FIG. 3, the shaft 218 is provided with a rotor positionsensor 224 for detecting the position of a pole of the rotor 250, and arotation speed sensor 226 for detecting the rotation speed of the rotor250. Outputs from the sensors 224 and 226 are taken into the controlcircuit 648 shown in FIG. 2. The control circuit 648 outputs a controlsignal to the drive circuit 653 based on the output taken. The drivecircuit 653 outputs the drive signal based on the control signal to thepower module 610. The power module 610 performs the switching operationbased on the control signal, and converts the direct-current powersupplied from the battery 180 into the three-phase alternating-currentpower. The three-phase alternating-current power is supplied to thestator windings 238 shown in FIGS. 3 and 4, so that a rotating magneticfield is generated in the stator 230. The frequency of the three-phasealternating current is controlled based on the detection value of therotation speed sensor 226. The phase corresponding to the rotor 250 ofthe three-phase alternating current is controlled based on the detectionvalue of the rotor position sensor 224.

FIG. 5A is a perspective view showing the rotor core 252 of the rotor250. The rotor core 252 consists of three cores 301, 302, and 301 asshown in FIG. 5B. The length H2 of the core 302 in the axial directionis set about twice as long as the length H1 of the core 301 in the axialdirection. FIG. 6 shows sections of the stator 230 and the rotor 250, inwhich FIG. 6A is a sectional view taken along the line A-A passingthrough the part of the core 301 (see FIG. 3), and FIG. 6B is asectional view taken along the line B-B passing through the part of thecore 302 (see FIG. 3). FIG. 6 omits the illustration of the housing 212,the shaft 218, and the stator winding 238. The rotor core 252 is made bylaminating a number of magnetic steel plates, for example, silicon steelplates, each having a thickness of 0.2 to 0.35 millimeters, like theabove-mentioned stator core. The lamination of thin steel plates cansuppress the occurrence of eddy current, thus reducing iron loss. Thereduction of iron loss is very important to the rotary electric machineused in the high-speed rotation region, like this embodiment.

A number of slots 24 and teeth 236 are evenly arranged along the entireperiphery of the stator core 232 on the inner peripheral side thereof,and the coil 233 is wound as shown in FIG. 4. In this embodiment, thenumber of slots is 72, but may be any other one. In FIG. 6, all slotsand teeth are not designated by reference numerals, and only parts ofthe teeth and slots are indicated as the representatives by therespective reference numerals. A slot insulator (not shown) is providedin the slot 24, and a plurality of phase windings of u to w phasesconstituting the stator windings 238 are mounted on the slots 24. Asmentioned above, this embodiment employs the distributed winding as theway to wind the stator windings 238.

The term “distributed winding” as used herein means a winding system inwhich the phase windings are wound around the stator core 232 such thateach phase winding is accommodated in two of the slots 24 spaced apartfrom each other via other slots. In this embodiment, the distributedwinding is used as the winding system, and thus the control can beperformed by using weak field magnet control and reluctance torque in awide range of the number of revolutions, including not only a lowrotation speed, but also a high rotation speed. As mentioned above, thereluctance torque is used to enable reduction of the magnet torque dueto the magnetic flux generated by the magnet, which can decrease theamount of permanent magnet material. As a result, the amount of magneticflux generated from the magnet is decreased, so that the induced voltagegenerated in the stator winding together with the rotation becomessmall. When the induced voltage generated in the stator winding 238 islarge, a difference between a voltage applied from the power converter600 to the rotary electric machine 200 or 202 and the induced voltagebecomes small, which makes it difficult to supply the alternatingcurrent from the power converter 600. In this embodiment, the use of thereluctance torque can reduce the induced voltage generated in the statorwinding 238, so that the alternating current can be supplied from thepower converter 600 to the stator winding 238 even in the high-speedrotation region, thereby enabling generation of rotary torque at therotary electric machine.

Each of the cores 301 and 302 of the rotor core 252 has holes 310 intoeach of which a magnet having a magnetic section shown in FIG. 6, thatis, a substantially rectangular or fan-shaped section at a surfaceperpendicular to the rotation axis is inserted. The holes 310 are formedat even intervals along the entire periphery of the rotor as shown inFIG. 5. The permanent magnet 254 is embedded in each hole 310, and fixedthereto by an adhesive or the like. The width of the hole 310 in thecircumferential direction is set larger than that of the permanentmagnet 254 in the circumferential direction, and the magnetic air gaps257 are formed on both sides of the permanent magnet 254. The magneticair gap 257 may have the adhesive embedded therein, or may be integrallyfixed together with the permanent magnet 254 by resin, or may be ahollow air gap. The permanent magnet 254 acts as a field pole of therotor 250. In this embodiment, one permanent magnet forms one magneticpole, but a plurality of magnets may form one magnetic pole. Thepermanent magnets may be arranged in the direction of rotation, or maybe superimposed on each other in the radial direction. The permanentmagnets need to generate the magnetic flux having the same polarity inunits of magnetic pole, and are required to be magnetized in the samedirection in relation to the opposed stator. The increase in number ofmagnets for each magnetic pole can increase the total amount of magneticfluxes thereby to increase the magnet torque.

The magnetization direction of the permanent magnet 254 is the radialdirection. The magnetization direction is reversed every field pole.That is, the stator side surface of a permanent magnet 254 a is the Npole, and the axis side surface thereof is the S pole. The stator sidesurface of an adjacent permanent magnet 254 b is the S pole, and theaxis side surface thereof is the N pole. These permanent magnets 254 aand 254 b are alternately arranged in the circumferential direction. Inthis embodiment, twelve permanent magnets 254 are arranged at evenintervals, and the rotor 250 has twelve poles.

The permanent magnet 254 may embed the rotor core 252 aftermagnification. Alternatively, the permanent magnet 254 maybe insertedinto the rotor core 252 before magnification, and then may be magnifiedby applying a strong magnetic field. The permanent magnetic 254 aftermagnetization becomes a strong magnet. When the magnet is magnetizedbefore the permanent magnet 254 is fixed to the rotor 250, a strongattraction force is generated between the permanent magnet 254 and therotor core 252 in fixing the permanent magnet 254, and then acts tointerrupt the work. The strong attraction force may cause contaminants,such as iron powder, to adhere to the permanent magnet 254. Thus, thepermanent magnet 254 is inserted into the hole 310 of the rotor core252, and magnified after being fixed, which improves the productivity ofthe rotary electric machine.

The permanent magnet 254 can be made of a neodymium-based sinteredmagnet, a samarium-based sintered magnet, a ferrite magnet, aneodymium-based bonded magnet, or the like. In particular, theneodymium-based permanent magnetic has a strong magnetic force, and thusis suitable in use for the rotary electric machine for driving thevehicle which generates high torque. The residual reflux density of thepermanent magnet 254 is desirably about 0.4 to 1.3 T.

FIG. 7A is an enlarged view of the vicinity of the permanent magnet 254b whose section is shown in FIG. 6A. The core 301 of the rotor core 252is provided with slots for forming magnetic air gaps 258 a on thesurface of the rotor 250, in addition to the magnetic air gaps 257formed on both sides of the permanent magnet 254. The magnetic air gap257 is provided for reducing the cogging torque, and the magnetic airgap 258 a is provided for reducing the torque pulsation in energization.The magnetic air gap 258 a is arranged shifted rightward with respect tothe q axis serving as the center axis between the magnets.

FIG. 7B is an enlarged view showing the vicinity of the permanent magnet254 b whose section is shown in FIG. 6B. A core 302 shown in FIG. 7B hasmagnetic air gaps 258 b formed, instead of the magnetic air gaps 258 a.The magnetic air gap 258 b is arranged shifted leftward with respect tothe q axis. As shown in FIGS. 6 and 7, the core 301 and the core 302have the same sectional shape except for the positions of the magneticair gaps 258 a and 258 b.

The magnetic air gaps 258 a and 258 b have the symmetric positions andshapes to each other with respect to the q axis. That is, the thinsilicon steel plate (electromagnetic steel plate) constituting the core301 is turned upside down to be laminated on another steel plate,thereby to form the core 302. This can reduce a manufacturing costbecause a mold costs less. The positions of the holes 310 of each of thecores 301 and 302 in the circumferential direction are aligned with eachother without misalignment. As a result, each permanent magnet 254fitted in each hole 310 integrally penetrates each of the cores 301 and302 without being separated in the axial direction. It is apparent thatpermanent magnets 254 divided into may be provided so as to be laminatedin the axial direction of the holes 310.

When the rotating magnetic field is generated in the stator 230 by thethree-phase alternating current, the rotating magnetic field acts on thepermanent magnets 254 a and 254 b of the rotor 250 to generate themagnet torque. The reluctance torque in addition to the magnet torquealso acts on the rotor 250.

FIG. 8 is a diagram for explaining the reluctance torque. Generally, theaxis on which the magnetic flux passes through the center of the magnetis referred to as a “d axis”, and the axis on which the magnetic fluxflows from between poles of one magnet to between poles of anothermagnet is referred to as a “q axis”. At this time, a core portionbetween field poles is referred to as an “auxiliary salient pole 259”.Since the magnetic permeability of the permanent magnet 254 provided inthe rotor 250 is substantially the same as that of air, a d-axis portionis magnetically concave, and a q-axis portion is magnetically convex asviewed from the stator side. Thus, a core of the q-axis portion isreferred to as a salient pole. The reluctance torque is generated by adifference of permeability of magnetic flux between the d axis and the qaxis, that is, a salient pole ratio.

As mentioned above, the rotary electric machine of this embodiment is arotary electric machine using both magnet torque and reluctance torqueof the auxiliary salient pole. Torque pulsations from the magnet torqueand the reluctance torque are respectively generated. The torquepulsation includes a pulsation component generated in non-energizationand a pulsation component generated in energization. The pulsationcomponent generated in non-energization is generally called as coggingtorque. Most of the conventionally methods for reducing the torquepulsation as described in the related art takes into consideration onlythe cogging torque. However, in use of the rotary electric machine underload, the torque pulsation of a mixture of the cogging torque and thepulsation component in energization is actually generated.

Most of the methods for reducing such torque pulsation of the rotaryelectric machine take into consideration only the reduction of thecogging torque, and hardly consider the torque pulsation generated inenergization. Noise of the rotary electric machine occurs under no load,but under load in many cases. That is, in order to reduce noise of therotary electric machine, it is important to reduce the torque pulsationunder load. Only measures against the cogging torque are not sufficient.

Now, a method for reducing torque pulsation in this embodiment will bedescribed below.

(Magnet Torque)

First, the magnet torque will be described. FIG. 9 is a sectional viewof a simulation result of distribution of magnetic flux, taken along theline A-A, when no current passes through the stator winding 338, thatis, of magnetic flux provided by the permanent magnet 254. Innon-energization, the magnetic flux of the permanent magnetic 254short-circuits the end of the magnet. Thus, the magnetic flux generatedby the permanent magnet 254 hardly passes through the auxiliary salientpole 259 for allowing the magnetic flux on the q axis to passtherethrough. It is found that the magnetic flux also hardly passesthrough the magnetic air gap 258 a provided slightly shifted from themagnetic air gap 257 of the end of the magnet. The magnetic flux passingthrough the stator 232 leads to the teeth 236 through the core on thestator side of the permanent magnet 254.

The same distribution of magnetic flux as that on the sectional viewtaken along the line A-A is also obtained on a sectional view takenalong the line B-B. The magnetic flux never passes through the auxiliarysalient pole 259 for allowing the magnetic flux on the q axis to passtherethrough, and hardly passes through the part of the magnetic air gap258 b. Thus, the magnetic air gaps 258 a and 258 b have little influenceon the magnetic flux associated with the cogging torque innon-energization. As a result, the magnetic air gaps 258 a and 258 bhave little influence on the cogging torque.

FIG. 10A shows a waveform of cogging torque actually measured, and FIG.10B shows a waveform of induced voltage generated on the stator sidewhen the rotor 250 rotates. The lateral axis indicates a rotation angleof the rotor in terms of electrical angle.

The line L11 indicates the rotor without the magnetic air gap 258, theline L12 indicates the rotor provided with the magnetic air gap 258 a,and the line L13 indicates the rotor provided with the magnetic air gap258 b. As can be seen from the result shown in FIG. 10B, the presence orabsence of the magnetic air gaps 258 a and 258 b hardly have influenceon the cogging torque.

The induced voltage is a voltage generated by causing the magnetic fluxof the magnet of the rotating rotor 250 to intersect the stator windings238. However, as shown in FIG. 10B, the waveform of the induced voltagehas a sine wave shape without being influenced by the presence orabsence of the magnetic air gaps 258 a and 258 b. The induced voltagereflects the magnetic flux of the magnet shown in FIG. 9. The fact thatthe induced voltage hardly changes means that the magnetic air gaps 258a and 258 b hardly have any influence on the magnetic flux of themagnet.

(Reluctance Torque)

Now, influences of the magnetic air gaps 258 a and 258 b on thereluctance torque will be described below. FIGS. 11 and 12 show magneticfluxes in energization. FIG. 11 is a sectional view taken along the lineA-A, and FIG. 12 is a sectional view taken along the line B-B. Therotary electric machine of this embodiment is a motor having 6 slots perone pole. The coils 233 of the stator windings 238 provided in the slots24 of the stator core 232 are divided into two layers in the directionof depth of the slot. When a slot adjacent to the coil 233 disposed onthe bottom side of the corresponding slot is countered as the firstslot, each coil 233 is inserted into another slot on the rotor side ofthe sixth slot 24 across first to fifth slots, which is fractional pitchwinding. The fractional pitch winding can reduce higher harmonic of amagnetomotive force of the stator, and has a short coil end and a littlecopper loss. Such winding for reduction of the higher harmonic canlessen the sixth torque pulsation specific to the three-phase motor, sothat only the twelfth pulsation component remains.

As can be seen from FIGS. 11 and 12, many magnetic fluxes pass throughthe q axis, and the magnetic air gaps 258 a and 258 b allow manymagnetic fluxes to flow therethrough. This is because the current of thestator 230 makes magnetic fluxes on the q axis. Thus, the magnetic airgaps 258 a and 258 b located at the auxiliary salient poles exert amagnetic influence in energization.

FIG. 13 shows the level of torque pulsation calculated per unit axiallength. The line L21 indicates the case where the magnetic air gap 258is not formed, the line L22 indicates the case where the magnetic airgap 258 a is formed, and the line L23 indicates the case where themagnetic air gap 258 b is formed. The line L24 indicates the torquepulsation in this embodiment employing the rotor 250 with the rotor core252 shown in FIG. 5. As mentioned above, in the rotary electric machineof this embodiment, a twelfth component of torque pulsation, that is, acomponent having 30 degrees as one cycle in terms of electrical angle ispredominant. As can be seen from FIG. 13, the twelfth component ispredominant, and the sixth component hardly exists.

The case of forming the magnetic air gap 258 a, and the case of formingthe magnetic air gap 258 b are found to cause the waveform of the torquepulsation to change with respect to the torque pulsation obtained whennot forming the magnetic air gap 258. This means that the magnetic fluxin energization is influenced by the magnetic air gaps 258 a and 258 b.The waveform in forming the magnetic air gap 258 a has a phasesubstantially opposite to that of a waveform in forming the magnetic airgap 258 b. As shown in FIG. 5, the ratio of the axial length of the core301 to that of the core 302, which constitute the rotor 250, is set toabout 1:2, so that the total torque pulsation L24 received by the entirerotor is an average of the torque pulsations indicated by the lines L22and L23. The total torque pulsation L24 is found to be small withrespect to the case in which the magnetic air gap 258 is not provided.

In this way, in this embodiment, the provision of the above magnetic airgaps 258 a and 258 b can reduce the torque pulsation in energization. Inorder to obtain such an effect, the width angle (the angle in thecircumferential direction) of the slot forming the magnetic air gap 258is preferably set equal to or less than half an angle of the auxiliarysalient pole in the circumferential direction.

The formation of the magnetic air gaps has the advantage of notdecreasing the torque as compared to the case in which no magnetic airgap is provided. Conventionally, a structure with skew for reducingtorque pulsation results in a decrease in torque by the skew. This makesit difficult to downsize the conventional rotary electric machinestructure. However, this embodiment can reduce only the torque pulsationof the reluctance torque, separately from the cogging torque, which hasthe advantage that the torque itself is not reduced. This is because thetoque pulsation in the rotor without slots has the predominant twelfthcomponent, and because the fractional pitch winding of the statorwindings is implemented.

(Reduction of Cogging Torque)

As mentioned above, the formation of the magnetic air gaps 258 a and 258b does not have any influence on the cogging torque in non-energization.Thus, the conventional method for reducing the cogging torque can beapplied to reduce the cogging torque, separately from the reduction ofthe torque pulsation in energization. In this embodiment, the followingarrangement can also reduce cogging torque.

FIGS. 14 and 15 are diagrams for explaining the method for reducing thecogging torque. FIG. 14 is a sectional view of parts of the rotor 250and the stator core 232. In FIG. 14, τp is a polar pitch of thepermanent magnet 254, and τm is a width angle of the permanent magnet254. Further, τg is an angle formed by combination of the permanentmagnet 254 and the magnet air gaps 257 provided on both sides thereof,that is, a width angle of the hole 310 as shown in FIG. 5. Thus, thecogging torque can be reduced by adjusting the angle ratio of τm/τp, andthe angle ratio of τg/τp. In this embodiment, the ratio of τm/τp ishereinafter referred to as a magnet pole arc degree, and the ratio ofτg/τp as a magnet hole pole arc degree.

FIG. 15 is a diagram showing the relationship between the ratio ofmagnet pole arc degree τm/τp and the cogging torque. The result shown inFIG. 15 is obtained in the case of τm=τg. In FIG. 15, the longitudinalaxis indicates an amplitude of cogging torque, and the lateral axisindicates a rotation angle of the rotor 250 in terms of electricalangle. The level of the amplitude of pulsation changes depending on theratio of τm/τp. For τm=τg, when the τm/τp is selected to be about 0.75,the cogging torque can be reduced. The tendency that the magnetic airgap 258 shown in FIG. 10 does not change the cogging torque can also beapplied to any case where the ratio of the magnet width to the polepitch, that is, τm/τp takes any value as shown in FIG. 15, in the sameway. Thus, under the above-mentioned conditions, the shape of the rotor250 is set to that shown in FIG. 5 or 6, which can reduce both thecogging torque and torque pulsation in energization.

In an example shown in FIG. 14, the following is set: τm/τp=0.55, andτg/τp=0.7. In this case, these values are optimal for simultaneouslyreducing the cogging torque in non-energization and the torque pulsationin energization. In this example, the magnet has a fan-like shape. Whenthe magnet has a rectangular shape, such values are slightly changed,which is apparently within the same scope of the invention.

(Effective Use of Reluctance Torque)

In the example shown in FIG. 15, the relation of τm=τp is satisfied asdescribed above. In order to effectively use the reluctance torque,which is an effect of the auxiliary salient pole 259, the magnet holepole arc degree τg/τp may be preferably set to about 0.5 to 0.9, andmore preferably to about 0.7 to 0.8.

FIG. 16 shows a calculation example of the maximum torque obtained bychanging the magnet pole arc degree τm/τp and the magnet hole pole arcdegree τg/τp. The lateral axis indicates the magnet hole pole arc degreeτg/τp. FIG. 16 shows that the magnet hole pole arc degree τg/τp of 0.7corresponds to the ratio of the auxiliary salient pole 259 to a pitchbetween poles of 0.3. The magnet width τm cannot be larger than anopening angle τg of the magnet hole, leading to τg≧τm. As the τm isincreased, the width of the permanent magnet 254 is increased, therebyincreasing the torque. On the other hand, when the τm is constant, theτg is an optimal value. When the ratio of τg/τp is about 0.7 to 0.8, themaximum torque becomes largest. This is because the size of theauxiliary salient pole 259 can take an appropriate value, and becausethe reluctance torque becomes small when the value of τg is much largeror smaller than the appropriate value. When the value of τm is largerthan 0.75, ρm=τg is desirable so as to make the auxiliary salient pole259 as large as possible.

In this way, when τg/τp is about 0.7 to 0.8, the reluctance torque canbe used most efficiently, which can make the permanent magnet 254 small.In use of a rare-earth sintered magnet as the permanent magnet 254, themagnet is required to be used most efficiently in terms of amountbecause the sintered magnet is very expensive as compared to othermaterials. Since the permanent magnet 254 is small, the induced voltagedue to the magnetic flux of the permanent magnet 254 can be lessened, sothat the rotary electric machine can be rotated at higher speed. Thus,the electric vehicle uses the rotary electric machine using thereluctance torque like this embodiment as a rotary electric machine fordriving the electric vehicle, thereby to obtain preferable properties.

[Explanation about Shift of Magnetic Air Gaps 258]

In the above description about the embodiments, the magnetic air gaps258 are arranged in two different positions. That is, provision of themagnetic air gaps 258 a and 258 b in different positions reduces thetorque pulsation in energization. Now, the way to shift the magnetic airgap 258 for reducing the torque pulsation will be described below.

A structure with a magnet skewed is conventionally known as means forreducing the torque pulsation. The inventors have found through studiesthat this concept of skew can be applied to the shift of the magneticair gaps 258. First, the skew of the magnet will be described below.FIGS. 17A and 17B are perspective views for explaining the concept ofthe rotor 250 with skew, in which FIG. 17A shows the case in which therotor 250 is divided into two parts in the axial direction, and FIG. 17Bshows the case in which the rotor 250 is divided into three parts in theaxial direction. FIG. 17 is a schematic diagram showing an example inwhich the permanent magnet 254 is provided on the surface of the rotor.The same can go for a rotor in which a permanent magnet is embedded. InFIG. 17, the reference numeral θ indicates an angle of skew. In theexample shown in FIG. 17B, the center core is skewed by the angle θ withrespect to the cores on both ends.

Among various methods for skewing, four kinds of methods for skewing bylaminating the cores as shown in FIG. 17 will be described below withreference to FIG. 18. In any one of cases shown in FIGS. 18A to 18D, arotor core 252 is divided into eight cores having the same thickness inthe axial direction. As shown in FIGS. 18A to 18C, when the skewingoperation is performed in two stages, the skew angle θ is normally setto be 15 degrees or 30 degrees in terms of electrical angle. Whensetting a mechanical skew angle θ, a phase shift needs to be performedbased on the electrical angle corresponding to the skew angle θ. In thefollowing, the skew in terms of electrical angle will be describedbelow.

The reason for setting the skew angle θ to 15 degrees or 30 degrees interms of the electrical angle is that the three-phase motor normallyincludes sixth and twelfth torque pulsations for an electric frequency,and that the reduction of the torque pulsation needs skewing by such anangle. For example, when the sixth torque pulsation is a primarycomponent of torque pulsation having a cycle of 60 degrees in terms ofthe electrical angle, a half cycle of the torque pulsation correspondsto 30 degrees in terms of electrical angle. Thus, when the skew angle θof the core corresponds to the electrical angle of 30 degrees in skewingthe divided cores, the primary components of the torque pulsations inthe cycle of 60 degrees, which pulsations are generated in tworespective cores shifted from each other, have reverse phases to eachother, and act to cancel the respective pulsations to each other. As aresult, the total torque pulsation is reduced.

Thus, the cores into which the rotor 250 is divided are shifted by 30degrees in terms of the electrical angle as mentioned above, which canreduce the primary component of the torque pulsation. Likewise, in thecase of the third component, since one cycle corresponds to 20 degreesin terms of electrical angle, 30 degrees in terms of electrical anglecorresponds to one and half cycle. Further, likewise, in the case of thefifth component, 30 degrees in terms of electrical angle corresponds totwo and half cycles. Thus, like the first component, the torquepulsations are substantially cancelled each other, so that the totaltorque pulsation is reduced. Also, the same goes for a seventh or moreodd-numbered component, and the cores are skewed by 30 degrees in termsof electrical angle, which can reduce the odd-numbered component of thetorque pulsation.

However, when the cores are shifted by 30 degrees in terms of electricalangle, even-numbered components, such as secondary, fourth, and thelike, of the torque pulsation generated from the cores have theidentical cycle to each other to increase the amplitude of the totaltorque pulsation. Thus, when the secondary component of the torquepulsation is smaller than the primary component thereof, shifting of thecores by 30 degrees in terms of electrical angle has an effect ofreducing the torque pulsation. Conversely, when the primary component ofthe torque pulsation is smaller, and the secondary component thereof islarger than the primary component, shifting of the cores by 15 degreesin terms of electrical angle is very effective for reduction of thetorque pulsation. For example, in the case of the secondary component,60 degrees in terms of electrical angle corresponds to two cycles. Thus,the shifting of the cores by 15 degrees in terms of electrical anglecorresponds to a phase shift of 0.5 cycle, so that the torque pulsationscancel each other.

In the examples shown in FIGS. 18A to 18C, the skew is performed in twostages, and in the example shown in FIG. 18D, the skew is performed inthree stages. The permanent magnet 254 may not be divided in the axialdirection in a block not skewed, or may be divided into a plurality ofparts. In the example shown in FIG. 18D, a shift angle between theadjacent cores is set to 10 degrees or 20 degrees in terms of electricalangle. When the primary component is the sixth torque pulsation, thatis, torque pulsation in a cycle of 60 degrees in terms of electricalangle, the shifting of the cores by 10 degrees or 20 degrees in terms ofelectrical angle allows the primary component to be shifted by one sixthof a cycle or one third of a cycle. In the skew method of shifting byone third of a cycle, a 3n-th component of the torque pulsation remains,but other components disappear. This method lessens the torque pulsationas compared to the above-mentioned general method using the reversephases.

In the examples shown in FIGS. 18A to 18C, an excitation force isapplied in the axial direction in driving the motor. In the method shownin FIG. 18D, the excitation force is not generated axially. Thus, novibration is applied to the external part of the rotary electricmachine, which makes the rotary electric machine silent. Also, in thiscase, when the primary component of the torque pulsation is small andthe secondary component thereof is predominant, skewing may preferablybe performed by 10 degrees, and not 20 degrees. In anyone of cases shownin FIGS. 18A to 18D, the total axial thickness of the cores with thesame shift angle is equal regardless of the shift angle. As long as thetotal axial thickness of the cores with the same shift angle is constantregardless of the shift angle, the method for shifting cores is notlimited to the methods shown in FIGS. 18A to 18D, and may be anycombination of methods for shifting cores.

In the above description, the stator core, that is, the permanent magnet254 is skewed thereby to reduce the sixth toque pulsation of thethree-phase motor, for simplification. The inventors considered that thepulsation due to the rotating magnetic flux made by the stator currentusing the magnetic air gaps 258 can be handled by introducing theabove-mentioned concept of the means for skewing with skew by the magnet(see FIG. 18).

For example, the inventors have found through studies that thecombination of the above-mentioned cores 301 and 302 shown in FIG. 5 canbe basically applied to the case shown in FIG. 18A. That is, as shown inFIG. 13, the cycle and amplitude of torque pulsation generated in thecores 301 and 302 with the magnetic air gaps 258 a and 258 b formedtherein may be actually examined, and the positions of the cores 301 and302 may be found in such a manner that the torque pulsations due to therespective cores have reverse phases from each other, or are shiftedfrom each other by one third of a cycle. Then, the cores 301 and 302 maybe disposed such that the total torque pulsation is reduced.

Furthermore, the conventional stage skew for axially dividing the magnetand the simulated skew for shifting the magnetic air gaps 258 providedin the auxiliary salient pole 259 may be used together. For example, theprimary component of the torque pulsation in a cycle of 60 degrees iselectrically cancelled by shifting the permanent magnets 254 from eachother by 30 degrees in terms of electrical angle, and the secondarycomponent of the torque pulsation in a cycle of 30 degrees is cancelledby the simulated skew of the magnetic air gaps 258.

In the above-mentioned embodiment, the skew structure for shifting instages as shown in FIG. 18 is employed so as to prepare only one type ofmold for forming the rotor core 252 using a silicon steel plate.Alternatively, as shown in FIGS. 19A and 19B, a skew structure may betaken so as to have the continuously shifted magnetic air gap 258. Inthe figure, the case of 60 degrees is to reduce the odd-numberedcomponent of the torque pulsation, while the case of 30 degrees is toreduce the even-numbered component of the pulsation. In any case, themagnetic air gap 258 is shifted so as to continuously change the cycleof the pulsation from zero to one cycle.

FIG. 20 shows the case where this embodiment is applied to a surfacemagnet type rotor. A method for fixing the magnets 254 (254 a, 254 b) tothe rotor core 252 may include fixing with an adhesive. Another methodmay include holding a tape on the surface of a rotor by winding the tapeon the rotor surface. An auxiliary salient pole 259 is provided betweenthe permanent magnets 254, and a slot is formed as a magnetic air gap258 a in a position shifted from the center of the auxiliary salientpole 259 (on the q axis). FIG. 20 shows a section of the rotor takenalong the line A-A. In the section taken along the line B-B, a magneticair gap (slot) 258 b is formed in a position symmetric to the magneticair gap 258 a, like the above-mentioned embodiment.

In the example shown in FIG. 20, the slot is provided in the auxiliarysalient pole, but the auxiliary salient pole itself may be bilaterallyasymmetric. The sectional shape of the permanent magnet 254 is an arcshape on the stator core side, but maybe linear. Conventionally, such asurface magnet type motor reduces the torque pulsation by means of acurvature radius of the permanent magnet 254 on the outer peripheralside. Provision of the magnetic air gaps 258 of this embodiment in sucha motor structure can reduce higher level torque pulsation.

FIG. 21 shows the concentrated winding of stator windings 238 shown asthe example in FIG. 20. Torque pulsation in this embodiment depends onthe shape of the rotor 250. Thus, even the concentrated winding system,which is different from the above-mentioned winding system on the statorside, can reduce the torque pulsation, like the case described above.

(Explanation of Effects)

The above-mentioned rotary electric machine of this embodiment has thefollowing operation and effects.

(1) The magnetic air gaps 258 a and 258 b are provided in the auxiliarysalient poles 259. The magnetic air gaps 258 a and 258 b are arranged tobe shifted from each other such that the torque pulsations caused by thegaps 258 a and 258 b in energization cancel each other as shown in FIG.13. As a result, the torque pulsation of the rotary electric machine canbe reduced in energization. In particular, the rotary electric machineof this embodiment that can reduce the torque pulsation in energizationcan be used as a motor for traveling an electric vehicle or the like toreduce vibration and noise in low-speed acceleration, which can providethe electric vehicle with good ride quality and high level of silence.(2) As shown in FIG. 9, in non-energization, the magnetic air gap 258has little influence on the magnetic flux. Thus, measures for reducingthe cogging torque due to the magnetic flux of the permanent magnet 254,and measures for reducing the torque pulsation in energization can beindependently taken. As a result, both optimization of the magnet torqueand reduction of the torque pulsation in energization can be achieved soas to lessen the cogging torque and increase the torque in energization.Conventionally, the magnet is constructed so as to maximize the torque,and thereafter the skew or the like is provided so as to lessen thecogging torque, which results in reduced torque (magnet torque).However, this embodiment can avoid reduction of torque caused due toreduction of the torque pulsation.(3) As mentioned above, since reduction of the magnet torque togetherwith the reduction of torque pulsation can be prevented, the magnet canbe made as small as possible, which can achieve reduction in size andcost of the rotary electric machine.(4) Since the positions of the magnetic air gaps 258 a and 258 bprovided in the auxiliary salient poles 259 are shifted from each otherto reduce the torque pulsation in energization, the permanent magnet 254does not need to be axially divided into a plurality of parts andmagnetized while being skewed, unlike the conventional skew structure. Arare-earth magnet, typified by a neodymium-based magnet, for example, isused for the permanent magnet 254, and is subjected to grinding to beshaped. Thus, the accuracy for preventing a manufacturing error isenhanced, which directly leads to an increase in cost. Thus, accordingto this embodiment which does not need dividing the magnet in the axialdirection, the cost of the rotary electric motor can be reduced. Thus,the accumulation of tolerances of the magnets does not increasevariations in properties of the rotary electric machines, and does notdeteriorate yield ratios of the machines. In this way, this embodimentcan achieve improvement of productivity of the rotary electric machine,and also reduction in manufacturing cost.(5) A leakage of magnetic flux of the field pole can be reduced by themagnetic air gap 257 to improve the efficiency of the rotary electricmachine. As mentioned above, the magnetic air gap 257 has an effect ofreducing the cogging torque. Further, the magnetic air gap 257 hasanother effect of reducing the leakage of magnetic flux from thepermanent magnet. Now, the effect will be described using FIG. 9. Thepermanent magnets 254 s and 254 b has an N/S pole on the stator 230side, and a reverse S/N pole on the center side of the rotor. A magneticcircuit for short-circuiting of a portion between the poles of thepermanent magnet 254 via the auxiliary salient pole 259 can begenerated. The short-circuited magnetic flux does not contribute to themagnet torque, leading to reduction in efficiency of the rotary electricmachine. Provision of the magnetic air gap 257 can form a narrow andlong magnetic passage (magnetic bridge) between the magnetic air gap 257and the outer periphery of the rotor along the direction of rotation (inthe peripheral direction). As shown in FIG. 9, the provision of themagnetic air gap 257 can form the magnetic bridge, thereby reducingleakage magnetic fluxes. The sectional area of the magnetic circuit ofthe magnetic bridge is small, and thus the magnetic circuit is broughtinto a magnetic saturation state, whereby the amount of magnetic refluxpassing through the magnetic bridge can be reduced thereby to improvethe efficiency of the rotary electric machine. The amount of magneticreflux passing through the magnetic bridge can be decreased, which makesthe influence of the magnetic air gap 258 on the cogging torque verysmall. The magnetic air gap 257 can have various shapes, and further canhave a shape with a curved line. This shape is formed so as to avoidconcentration of mechanical stress, whereby the mechanical stress isonly slightly concentrated, so that the sectional area of the shape canbe made small to reduce the leakage magnetic flux.

Second Embodiment

FIGS. 22 to 24 are diagrams for explaining the second embodiment of theinvention.

FIG. 22A is a sectional view of the rotor 250 corresponding to thesection taken along the line A-A shown in FIG. 6A, and FIG. 22B is asectional view of the rotor 250 corresponding to the section taken alongthe line B-B shown in FIG. 6B. That is, also in the second embodiment,the rotor core 252 is constructed of three cores as shown in FIG. 5.FIG. 22A shows the section of the core 301, and the FIG. 22B shows thesection of the core 302. In the above example shown in FIG. 6, themagnetic air gaps 258 are formed as the slot on the surface of the rotorcore 252. In the second embodiment, the air gaps 258 are formed insidethe rotor core 252.

The sectional shape of the permanent magnets 245 (254 a, 254 b) isrectangular, and the magnetic air gap 258 is provided so as to be incontact with one side of the field pole made by the permanent magnets245 (254 a, 254 b). In FIG. 22A, a magnetic air gap 258 a is provided soas to be in contact with one side of the permanent magnet 254 in thecircumferential direction. In FIG. 22B, a magnetic air gap 258 b isprovided so as to be in contact with the other side of the permanentmagnet 254 in the circumferential direction. Also in this case, thepermanent magnet 254 is located at the center on the d axis. Themagnetic air gap 258 a is disposed shifted toward the permanent magnet254 a with respect to the center (q axis) of the auxiliary salient pole259, and the magnetic air gap 258 b is disposed shifted toward thepermanent magnet 254 b with respect to the q axis.

Also, in the second embodiment, different torque pulsations aregenerated in the core 301 and in the core 302. These pulsations act tocancel each other, thereby enabling reduction of the total torquepulsation. Like the first embodiment, the magnetic air gap 258 is formedin the auxiliary salient pole 259, which has little influence on thecogging torque. That is, the magnetic air gap 258 is provided tosuppress the influence of the cogging torque on reduction of thepulsation, and thus can reduce the torque pulsation in energizationsubstantially separately from the cogging torque pulsation. The use ofthe permanent magnet 254 having a rectangular section can reduce aprocessing cost of magnets.

The example shown in FIG. 23 is a modified one of the rotor 250 shown inFIG. 22.

In the example shown in FIG. 22, one of the sides of the permanentmagnet 254 is in contact with the rotor core 252, and the other of thesides thereof is in contact with the magnetic air gap 258. Thus, theother side of the permanent magnet in contact with the magnetic air gap258 allows the short-circuited portion of the magnet magnetic flux to beshifted toward the magnetic air gap 258, so that the center of themagnet is shifted from the center of the magnetic flux of the magnet. Inthe example shown in FIG. 23, a bridge 260 constructed of the rotor core252 is provided between the permanent magnet 254 and the magnetic airgap 258. In this way, the magnetic flux is also short-circuited by thebridge 260 on the magnetic air gap side, thus allowing the magnetic fluxto leak in the same manner as that on the other side of the permanentmagnet 254. Thus, routes for short-circuiting the magnetic fluxes onboth sides of the permanent magnet 254 are the same to each other, andthus can more reduce the influences of the magnetic air gap 258 on thecogging torque and induced voltage.

FIG. 24 is a diagram of another example of the second embodiment,showing a plurality of permanent magnets 245 provided on the respectivepoles of the rotor 250. The rotor 250 and the entire rotary electricmachine including the stator and the sensor have the same structures andalso the same basic operations and effects as those described above,except for the permanent magnets 254 a and 254 b constituting therespective field poles, or the magnetic air gap 257 for reducing thecogging torque or leakage magnetic flux, or the magnetic air gap 258 bfor reducing pulsation due to the rotating magnetic field made by astator current. In the example shown in FIG. 24, the permanent magnetsfor forming field poles are constructed of a plurality of permanentmagnets 254 (two magnets in this embodiment) disposed in a V shape. Thesectional view shown in FIG. 23 corresponds to the sectional view takenalong the line B-B shown in FIG. 6B. A pair of permanent magnets 254 aand a pair of permanent magnets 254 b correspond to the permanentmagnets 254 a and 254 b shown in FIG. 6B. A core portion between amagnetic pole made by each of the permanent magnets 254 a arranged inthe V shape and a magnetic pole made by each of the adjacent permanentmagnets 254 b arranged in the V shape serves as the auxiliary salientpole 259, and the q axis is located at the center of the auxiliarysalient pole 259.

Magnetic air gaps 257 for treating cogging torque are respectivelyprovided on both ends in the circumferential direction of the permanentmagnet 254 having a rectangular section, like the rotor 250 shown inFIG. 6. Also, in the rotor 250 shown in FIG. 24, the magnetic air gap258 b is provided in the rotor core 252, and is arranged shifted towardone side (left side) in the rotation direction (circumferentialdirection) with respect to the q axis provided at the center of theauxiliary salient pole 259. The effect of suppressing the torquepulsation by the magnetic air gap 258 b becomes higher as the magneticair gap 258 b is located closer to the surface of the rotor core 252.The rotor core is disposed in the magnetic air gap 258 b to be shiftedtoward one side (left side) in the rotation direction with respect tothe q axis provided at the center of the auxiliary salient pole 259. Arotor core (not shown) is disposed in the magnetic air gap 258 a to beshifted toward the other side (right side) in the rotation directionwith respect to the q axis provided at the center of the auxiliarysalient pole 259. These rotor cores are arranged along the rotation axisas explained in FIGS. 18 and 19. Thus, the pulsations generated in therotor cores are cancelled each other, which can reduce the totalpulsation.

In the example shown in FIG. 24, the auxiliary salient pole 259 iswidened, so that the reluctance torque can be used more effectively. Amagnet hole for accommodating therein the permanent magnet 254 is formedto make the bridge 260 narrow such that the magnetic flux of thepermanent magnet 254 does not run around and enter the core. Althoughthe magnetic air gap 258 b is provided in the rotor core 252, a concaveportion (slot) may be provided as the magnetic air gap 258 b on thesurface of the rotor core 252, like the first embodiment. The structurehaving the section as shown in the sectional view taken along the lineA-A is the same as the section shown in the sectional view taken alongthe line B-B in FIG. 24, except that the magnetic air gap 258 a isprovided in a position symmetric to the q axis. Thus, as mentionedabove, the description and illustration thereof will be omitted.

In other example, the V shaped magnet structure includes doublysuperimposed magnets. The magnetic air gaps 258 are arranged shifted inthe auxiliary salient pole 259 with respect to the q axis to reduce thetorque pulsation. This effect does not apparently change regardless ofthe arrangement of the permanent magnets 254. In FIG. 24, a magnetic airgap 258 a is provided adjacent to the magnetic air gap 257. A slot likethe first embodiment may be provided, or the magnetic air gap 257 andthe magnet air gap 258 a may be integrated.

Third Embodiment

FIG. 25 shows a rotor 250 according to a third embodiment. FIG. 25A is asectional view corresponding to the sectional view taken along the lineA-A shown in FIG. 6A, and FIG. 25B is a sectional view corresponding tothe sectional view taken along the line B-B shown in FIG. 6B. In theexample shown in FIG. 25, two kinds of magnetic air gaps per one poleare provided. That is, a pair of magnetic air gaps 251 are also providedin the core on the outer peripheral side of the magnet, in addition tothe magnetic air gaps 258 in the auxiliary salient pole 259. Themagnetic air gaps 251 are symmetrically provided with respect to the daxis passing through the center of the permanent magnet. The magneticair gaps 251 may be provided asymmetrically. The magnetic air gap 251 ismainly provided for reducing the cogging torque, and thus is disposed inthe core on the outer peripheral side of the magnet through which themagnet flux passes. Such an arrangement can respectively reduce theprimary and secondary torque pulsations, and also the cogging torque andthe torque pulsation in energization.

The rotor 250 having slots formed as the magnetic air gap 258 on thesurface of the rotor core 252 can be cooled through the slots. As shownin FIG. 26, the rotary electric machine 200 is sealed in the housing234, in which oil 403 for cooling is charged so as to slightly cover therotor 250. The oil 403 circulates by a pump 402 for cooling and iscooled by a radiator 401. The rotor 250 has slots 257 which allow theoil to penetrate the core 302 located at the axial center shown in FIG.5. With the slant slots (magnetic air gaps 258) shown in FIG. 24, therotation of the rotor 250 allows the oil to enter the rotor thereby tocool the axial center of the rotor 250. A neodymium-based magnet has alow heatproof temperature of about 200° C., and thus demagnetized athigh temperatures, which is a problem from the viewpoint of downsizing.Thus, the provision of such a cooling route is effective for downsizingthe motor for the hybrid vehicle or the electric vehicle. Two or moretypes of magnetic air gaps 258 may be formed in the auxiliary salientpole 259. This can enhance flexibility of reduction of torque pulsation,and further can reduce the torque pulsation in more detail.

As mentioned above, in the embedded magnet type rotary electric machineof this embodiment using reluctance torque generated by the auxiliarysalient pole 259, the cores with the magnetic air gaps 258 are laminatedin the direction of lamination in respective positions shifted from theq axis which is the center of the auxiliary salient pole 259 toconstitute the rotor. The rotary electric machine can reduce the torquepulsation in energization separately from the reduction of pulsation ofthe cogging torque. As a result, such a rotary electric machine isapplied to the motor for traveling the electric vehicle or hybridvehicle, thus resulting in less vibration and noise in low-speedacceleration, thereby improving the ride quality and the level ofsilence.

Fourth Embodiment

A fourth embodiment of the invention will be described below using FIGS.27 to 32. FIG. 27 is a partial diagram of the outer appearance of arotor core 252. The rotary electric machine includes a core 301 havingthe rotor core 252 and a magnetic air gap (cutout) 258 formed on oneside thereof in the rotation direction with respect to the center of theauxiliary salient pole 259, and a core 302 having a magnetic air gap(cutout) 258 formed on the other end in the rotation direction withrespect to the center of the auxiliary salient pole 259. As described inFIG. 5, the length of the core 302 in the direction of the rotor isabout twice as long as that of the core 301. The rotary electric machinestructure is not limited thereto, and the shape and combination of thecores may be modified as explained with reference to FIGS. 17 to 19.Permanent magnets 254 a and 254 b inserted into the cores 301 and 302have substantially the same shape in the substantially same rotationposition. An integrated permanent magnet 254 may be inserted.Alternatively, a permanent magnet may be divided regardless of the cores301 and 302. The hole for insertion of the permanent magnet 254 and themagnetic air gap 257 in the core 301 have substantially the samerespective shapes and rotation positions as those of the hole and themagnetic air gap 257 in the core 302. These holes and air gaps arecontinuously formed in the direction of rotation axis.

In this embodiment, each field pole has one permanent magnet 254.Alternatively, as shown in FIG. 24, each field pole may have a pluralityof permanent magnets 254. An auxiliary salient pole 259 is providedbetween the adjacent field poles, and the above-mentioned magnetic airgap 257, the magnetic bridge 272, and the slot 282 are further providedbetween the auxiliary salient pole 259 and an area between the fieldpoles. A stator side core of each permanent magnet 254 serves as amagnet pole piece 262. The magnetic flux generated from the permanentmagnet 254 a is guided from the magnetic pole piece 262 formed on thestator side of the permanent magnet 254 a to the stator, and then guidedfrom the stator to the permanent magnet 254 b via the magnet pole piece262 formed on the stator side of the permanent 254 b. Theabove-mentioned permanent magnet 254 a and the permanent magnet 254 bare magnified to reverse polarities as described above.

Each magnetic bridge 272 provided between each field pole and theauxiliary salient pole 259 serves to lessen the magnetic fluxes whichleak from the magnetic pole piece 262 to the auxiliary salient pole 259,or serves to lessen the magnetic fluxes which leak from the magneticpole pieces 262 to the magnetic pole on the side opposite (on therotation axis side) to each permanent magnet 254. That is, when eachmagnetic bridge 272 is magnetically saturated, a magnetic resistancebecomes very large, and the magnet reflux passing is restricted.Further, in this embodiment, the slot 282 is provided to make themagnetic bridge 272 long, and to have a spring property, therebypreventing concentration of stress due to a centrifugal force. The slot282 has such a shape with a wide bottom 284 and with a curved surfacesimilar to an arc shape as to prevent concentration of the stress.

FIGS. 28 and 29, and FIGS. 30 to 32 show parts of sections perpendicularto the stator and the rotation axis of the rotor. FIGS. 30 to 32slightly differ from FIGS. 28 and 29 in the shape of the magnetic airgap 257, the magnetic bridge 272, and the slot 282, but have the samebasic concept as that of FIGS. 28 and 29. FIGS. 28, 30, and 32 show thestructure of the rotor core used in the core 301, and FIGS. 29 and 31show the structure of the rotor core used in the core 302. The basicstructures of FIGS. 28 to 32 are those such as described above withreference to FIG. 27. In these drawings, the magnetic air gaps 257 arerespectively provided on the auxiliary salient pole 259 of the permanentmagnet 254. The magnet air gap 257 extends in the rotation direction ofthe rotor to form the magnetic bridge 272 between the magnetic air gap257 and the surface of the rotor. The magnetic bridge 272 leads to themagnetic pole piece 262 via the air gap. The magnetic air gap 257extends in the rotation direction along the outer periphery of the rotor250 thereby to relieve a drastic change in magnetic flux density in therotation direction (circumferential direction) caused by the air gapbetween the rotor 230 and the rotor 250, thus reducing the coggingtorque.

The slot 282 is formed on the auxiliary salient pole 259 side of themagnetic bridge 272, and the magnetic bridge 272 directed in the radialdirection is formed between the magnetic air gap 257 and the slot 282.In these embodiments, the outer peripheral side of the magnetic bridge272 directed in the radial direction is directed in the direction of theline L2 with respect to the normal line L1 extending radially throughthe rotation axis. The length of the magnetic air gap 257 in the radialdirection is shorter than that of the permanent magnet 254 in the radialdirection. The magnet bridge 272 has its direction changed along theshape of the magnetic air gap 257 on the auxiliary salient pole 259side, and is directed in the direction of the line L3. The line L2 isdirected from the permanent magnet 254 to the auxiliary salient pole 259as the line L2 approaches the center of the rotor. That is, the line L2is directed such that a distance from the line L1 becomes wider in therotation direction as the line L2 approaches the center of the rotor.The line L3 is directed from the auxiliary salient polar 259 to thepermanent magnet 254 as the line L3 approaches the center of the rotor.That is, the line L3 is directed such that a distance from the line L1becomes narrower in the rotation direction as the line L3 approaches thecenter of the rotor. Thus, the magnetic bridge 272 changes from thedirection of the line L2 to the direction of the line L3 which isdirected opposed to the rotation direction with respect to the line L1.

The magnetic bridge 272 has such a shape to prevent the centrifugalforce with respect to the mass of the permanent magnet 254 and themagnetic polar piece 262 from being concentrated on a part of the bridge272, and thus has resistance to high-speed rotation. Conversely, themagnetic sectional area of the magnetic bridge 272 can be made small,which can reduce the leak magnetic flux, thereby improving the magneticproperties. The bottom 284 of the slot 282 is formed deeply in therotation axis direction with respect to the magnetic air gap 257, andexpands along the circumferential direction (rotation direction),facilitating the change from the direction of the line L2 of themagnetic bridge 272 to the direction of the line L3. Further, theconcentration of stress on the slot bottom 284 can be prevented.

As shown in FIGS. 28 and 29, the magnetic air gap 258 has a relativelysmall cutout, but as shown in FIGS. 30 to 32, the gap 258 has arelatively large cutout. FIG. 28 to FIG. 32 precisely illustrate thesizes of the rotor, the stator, and the slot, and the relationshipbetween the sizes of other components. The ratio θa/θm of an angle θa inthe rotation direction of the auxiliary salient pole 259 sandwichedbetween the slots 282 to an angle θm in the rotation direction of thepermanent magnet 254 is about 0.5 (θa/θm≅0.5). The ratio θc/θm of anangle θc in the rotation direction of the magnetic air gap (cutout) 258to the angle θm is about 0.5 (θc/θm≅0.5). This relationship is one ofexamples.

The condition of θa/θm is desirably more than 0.25 and less than 0.75(0.75>θa/θm>0.25). It is desirable that θc is larger than the opening onthe rotor side of each slot of the stator, and that θc/θm is smallerthan 0.7 (0.7>θc/θm). Further, the condition of θc/θm that is less than0.5 is optimal. The depth of the magnetic air gap 258 in the radialdirection is equal to or less than a half of the width of the permanentmagnet 254 in the radial direction.

The embodiments shown in FIGS. 27 to 32 have the operations and effectsexhibited by the above-mentioned embodiments. That is, the magnetic airgap 258 formed on the outer periphery of the auxiliary salient pole 259on the stator side can reduce the pulsation caused due to the rotatingmagnetic field generating stator current. The slot 282 is formed betweenthe magnetic air gap 258 and the permanent magnet 254 to reduce theamount of magnetic flux passing through the magnetic air gap 258 andgenerated by the permanent magnet 254 to a very small level, whereby theshape of the magnetic air gap 258 has very little influence on thecogging torque. In this embodiment, the magnetic air gaps 257 inaddition to the slots 282 exist, whereby the shape of the magnetic airgap 258 has very little influence on the cogging torque. This can reducepulsation due to the stator current by the above-mentioned solving meanswhich has a very little influence on the cogging torque.

The magnetic air gap 257 provided on the auxiliary salient pole 259 sideof each field magnetic pole of the rotor 250 further has an effect ofreducing the cogging torque.

The bridge 272 is formed along the magnetic air gap 257. The shape ofthe magnetic air gap 257 on the auxiliary salient pole 259 side can bemade by a combination of curved lines, or by a combination of a curvedline and a straight line. The shape of the magnetic bridge 272 on themagnetic air gap 257 side can be made into a curved shape, therebypreventing the concentration of stress. The magnetic bridge 272 isformed between the magnet air gap 257 and the slot 282, thereby enablingprevention of the concentration of stress. This can form the magneticbridge 272 having such a shape to endure a large centrifugal forcegenerated in the permanent magnet 254 and the magnet pole piece 262 inhigh-speed rotation.

In each of the above-mentioned embodiments, the motor for driving thevehicle has been described. The invention is optimally applied to therotary electric machine for driving the vehicle, but is not limitedthereto. The invention can be applied to various types of motors.Further, the invention can also be applied to various types of rotaryelectric machines, including a generator, such as an alternator, inaddition to the motor. The invention is not limited to the embodimentsdescribed herein without departing from the features of the invention.

1. A rotary electric machine comprising: a stator having stator windingswound in fractional pitch winding; a rotor rotatably disposed in thestator, said rotor having a rotor core, wherein the rotor core isdivided into a plurality of division cores provided in an axialdirection, each of said division cores having a plurality of magnets anda plurality of magnetic auxiliary salient pole portions formed betweenpoles of the magnets, and wherein a magnetic air gap is provided in theaxial direction of the rotor in a position shifted in a circumferentialdirection from a q axis passing through a center of a magnetic auxiliarysalient pole within the magnetic auxiliary salient pole portion, whereineach of the division cores have its own amount of shifting the magneticair gap from the q axis in the circumferential direction, and each ofthe amounts of shifting are set so as to reduce twelfth torquepulsation, which is a part of torque pulsation in energization of therotor.
 2. The rotary electric machine according to claim 1, wherein saidplurality of the division cores comprises first and second divisioncores with different said amounts of shifting, and wherein a differenceof the amounts of shifting between the first division core and seconddivision core is set so as to make the phase difference be 15 degrees interms of electrical angle between the torque pulsation in energizationof the first division core and the torque pulsation in energization ofthe second division core.
 3. The rotary electric machine according toclaim 1, wherein said plurality of the division cores comprises first,second, and third division cores with different said amounts ofshifting, and wherein the amounts of shifting of the first, the second,and the third division cores are set respectively so as to make thephase difference be 10 degrees or 20 degrees in terms of electricalangle between the torque pulsation in energization of the first divisioncore and the torque pulsation in energization of the second divisioncore, and between the torque pulsation in energization of the seconddivision core and the torque pulsation in energization of the thirddivision core.
 4. The rotary electric machine according to claim 1,wherein thicknesses in the axial direction of the respective divisioncores are substantially the same.
 5. The rotary electric machineaccording to claim 1, wherein the magnetic air gap is a concave portionformed at the surface of the rotor core, or a hole formed in the rotorcore.
 6. The rotary electric machine according to claim 5, wherein acircumferential angle of the concave portion is set equal to or lessthan one half a circumferential angle of an auxiliary salient pole. 7.The rotary electric machine according to claim 1, wherein the pluralityof magnets each of whose magnetization directions is a radial directionof the rotor core are arranged in the circumferential direction suchthat the magnetization directions are alternately reversed.
 8. Therotary electric machine according to claim 7, wherein the respectivemagnets constitute a magnet group including a plurality of magnets whosemagnetization directions are substantially equal.
 9. The rotary electricmachine according to claim 1, wherein the rotor core is formed bylaminating electromagnetic steel plates, each plate having a hole or acutout formed therein for forming the magnetic air gap.
 10. The rotaryelectric machine according to claim 9, wherein the two types of magneticair gaps located in different circumferential positions are formed inthe rotor core by laminating one steel plate on another steel plateturned upside down.
 11. The rotary electric machine according to claim1, wherein the magnets are shifted in a circumferential direction withrespect to their axial position.
 12. The rotary electric machineaccording to claim 1, wherein the stator windings are formed bydistributed winding.
 13. The rotary electric machine according to claim1, further comprises a housing containing the stator, the rotor, andcooling oil, wherein apart of the magnetic air gap provided in the rotorcore is soaked in the cooling oil.
 14. An electric vehicle comprising:the rotary electric machine according to claim 1; a battery forsupplying a direct-current power; and a converter for converting thedirect-current power of the battery into an alternating-current power,and supplying the alternating-current power to the rotary electricmachine, wherein the electric vehicle is traveled by a drive force ofthe rotary electric machine.